To some, lipos remain a murky area in airsoft. I started running lipos in 2008, well before I bought my first PTW, so there wasn’t any transition when Tac supplied my first Firefox 1200mAh 11.1v 20c lipos. I still use that type and brand, supplied by Tac – although I’m on my second set. Batteries are consumables, so they do need to be replaced periodically.
When I read Frank’s (Thundercactus) lipo primer on Tackleberry’s forum Facebook page this morning, it made me remember a few things I’d forgotten about lipos and joined the dots between other details. I think it’s a really useful resource and is refreshingly bullshit free.
I’ve reproduced it here, with permission. It’s wise and it’s well worth the read if, like me, you need to be spoon fed with a simplified version.
Following Frank’s words, there’s another primer: a short take on lipo vs NiCad, by none other than Canadian PTW guru Macguyver. Again, it’s essential reading.
“This is gonna be a long one. Scroll to the bottom for the summary!
I’ve been using LiPo for years, and they’ve gotten a lot of unnecessary flak and unwarranted bad reputation. The short of it is they’re not much more dangerous than NiMH or NiCd batteries. Of which I’ve seen more Ni batteries on fire (four of them) at airsoft games than LiPo (none).
Firstly, the C rating of a battery is ambiguous and means absolutely nothing on its own. Does. Not. Mean. Anything.
It’s like being asked “how much horsepower does that engine have?” and answering “it’s a 300CC”. Very little info. It could be an 8hp or 500hp engine, you have no idea.
So the function of the C rating is mathematical, it’s used to determine what kind of draw your battery can handle; Pack Amperage x C Rating = max continuous draw
So, a 1200mAh pack at 20C:
1.2A x 20C
= 24A max continuous draw
And a large battery example; 11.1v 4900mAh 20C (for my M249):
4.9A x 20C
= 98A max continuous draw
Now, your continuous draw rate has nothing to do with how much amperage goes to the motor. It’s simple an upper limit. A PTW motor generally draws up to 18A, so any pack that supplies at least 18A *should* be safe. I say anything 24A or more.
Whether you have 18A, 30A or 200A maximum continuous draw, the motor will only take 18A. Ever.
Now that being said, it’s totally true that you can run a PTW safely off a 1200mAh 20C pack or a 4900mah 5C pack or a 2200mAh 80C pack.
The C rating does not significantly affect your rate of fire. There will be minor difference between a 20C and 60C pack simply because of lower internal resistance of the pack itself, but both packs supply 12.6v at maximum, and the motor draws 18A no matter what. The only thing that changes is the resistance (ohms) on the circuit. Your ROF will be VERY comparable between 20C and 60C, so no reason to avoid it. I’d be surprised if you could even measure the ROF difference between a 20C and 25C pack.
Some people notice a difference in ROF going from 15C to 20C and assume that because the C rating is higher, it puts more current into the gun, and therefore they should stick to the 15C.
Extremely bad idea.
With the older Firefox batteries, the 1100mah 15C, it didn’t actually provide enough amperage to the motor (only 16.5A), and so the motor was starved of amperage and subsequently resulted in a lower rate of fire.
What most people don’t know is this causes over-current draw on a LiPo (where you try to pull more amperage than is safely possible) and it causes internal damage to the battery, typically causing it to get warm or swell. This later turns into a ball of seething fire when you go to charge it.
I’ve actually seen people use these batteries and seen them swell over time. It’s a miracle nobody’s house burned down.
Lots of issues with people running 11.1v LiPos and blowing their stock motors.
Ex; The previous owner of my PTW ran is for 3 years no problem with the NiCd battery, I used it for 2 games with an 11.1v LiPo and it blew a coil on the motor.
There’s some controversy about what exactly makes the LiPo harder on motors, but what’s fact is the NiCd battery supplies the same running amperage as a LiPo, so the motor’s not running with more amperage on a LiPo. BUT the LiPo is generally capable of supplying far more starting and stopping current than a NiCd. This is referred to as “burst rating”, another C rating but only for very short application. It’s generally 2x the normal C rating. So where you see a 1200mah 25-50C rating, that battery will be supplying up to 60A to the motor during it’s starting cycle and active braking. I’m just taking a stab at it but it makes sense to me that the extra current during rapid semi-auto fire would induce significantly more heat into the motor windings causing it to fail.
Also should note that just because a LiPo may not have a printed burst rating, does not mean that it’s incapable of burst current.
So to summarize;
-The C rating doesn’t mean anything on it’s own
-pack amperage x C rating = maximum safe continuous discharge
-Your LiPo must be able to supply at LEAST 18A max continuous draw for a PTW
-A LiPo battery should NEVER be hot to the touch or above room temperature or visibly swollen, this is an indication of internal damage and you must dispose of the battery IMMEDIATELY
-There’s almost no measurable difference between a 20C and 25C pack
-LiPo batteries do not explode. They smolder and vent and cause fires, but DO NOT explode.
-LiPo batteries only set ablaze when punctured, short circuited, or charged when they have internal damage.
-Always balance charge a LiPo, there’s absolutely no reason you shouldn’t, and it makes the charging experience MUCH safer.
-Do not exceed 4.2v/cell or go under 3.0v/cell or you’ll damage the battery
-Do not discharge LiPos, not only is it pointless as they don’t suffer from memory effects, but it’s also just plain dangerous.
-Do not use hand warmer packs on LiPo’s, they are not nickel chemistry packs, they perform just fine in the cold, they don’t need it”
You can read more on Airsoft Canada.
And so, onto lipo vs. NiCad.
Whilst Mac has simplified the motor physics, it’s under the bonnet gold to the layman:
“On the topic of Lipo vs. NiCad, it should be noted that the discharge curve on lipo is very flat, with a sudden drop when the battery is depleted. You could call it a constant voltage battery, since the voltage doesn’t really change dramatically, but the current delivery can drop steeply. For a NiCad battery, it can drop voltage in a more linear fashion as current drops.
In an eleectric motor, the windings are an inductor, and inductors can do some funny things when you starve them of current, as inductors generally try resist changes in current by trading voltage and charge inductance for current to stabilize their field.
In the case of Lipos, once that current disappears when the battery is depleted, the windings are not able to fully charge to generate the magnetic fields necessary to turn the motor. In fact, the windings themselves are essentially acting as simply a mass of copper wire, and are a short circuit rather than an inductor. Bursts of a dead short like that are going to make pre-existing problems like poor pole/comm joints, maybe bad Litz insulation on a winding segment or a stretched winding on a turn become a point of failure. Consider also that hammering these points with essentially full remaining discharge current, and failure would be inevitable.
It makes it worse when lipo can go from OK to dead withing a couple of shots if we rely solely on the sound we are used to from a motor slowdown when we used NiCads.”